This invention relates to the preparation of highly densified ceramic bodies by the pyrolysis of certain curable organopolysiloxanes filled with silicon carbide powders, organopolysiloxane curing agents, and certain metal-containing sintering aids. Such highly densified ceramic bodies can be prepared by either a pressureless sintering process or a hot press sintering process. This invention also relates to novel compositions of matter consisting essentially of silicon carbide powder, a metal-containing sintering aid, an organopolysiloxane curing agent, and a preceramic organopolysiloxane. These compositions of matter can be formed into desired shapes and then sintered to form ceramic, shaped bodies with high densities. One advantage of the present invention is that the green bodies have relative high strengths and thus can be easily handled and, if desired, machined before sintering. The green strength of the shaped bodies can be further increased by curing the formed body prior to sintering.
Prockazka in U.S. Pat. Nos. 4,004,934 and 4,041,117 and Prockazka et al. in U.S. Pat. No. 4,081,284 describe high density silicon carbide ceramic bodies prepared in a pressureless sintering process. Such ceramic bodies were prepared from mixtures consisting of silicon carbide powder, a boron-containing additive, and a carbonaceous additive. The carbonaceous additives or binders were high molecular weight, carbon-based aromatic compounds such as phenol-formaldehyde condensate-novolak, resorcinol-formaldehyde, aniline-formaldehyde, cresol-formaldehyde, derivatives of polynuclear aromatic hydrocarbon compounds contained in coal tar, polyphenylene, polymethylphenylene, and the like. Ceramic silicon carbide materials with greater than 85% of theoretical density were obtained.
Onda et al. in Japanese Kokai Pat. No. 60-16869 describe a method of preparing high density silicon carbide ceramics which involves pressureless sintering a mixture consisting of silicon carbide powder, an auxiliary sintering aid, and an organosilicon polymer characterized by a Si-C skeletal structure. Disclosed sintering aids include boron-, aluminum-, and beryllium-containing compounds. The organosilicon polymers were described as "high-molecular-weight organic silicon-containing compounds with silicon-carbon skeletal structures." The organosilicon polymers were not further identified even in the examples. Based on this limited description, however, it appears likely that the organosilicon polymers were polycarbosilanes which have a Si-C skeletal backbone.
The present invention provides high density ceramic products from a pressureless sintering process using curable organopolysiloxanes as binders. Generally, high density ceramic materials will possess high strengths.